In this
case we can clearly see that if we wished in imagination to give the
plant the power of increasing in number, we should have to give it
some advantage over its competitors, or over the animals which preyed
on it. On the confines of its geographical range, a change of
constitution with respect to climate would clearly be an advantage to
our plant; but we have reason to believe that only a few plants or
animals range so far, that they are destroyed by the rigour of the
climate alone. Not until we reach the extreme confines of life, in the
arctic regions or on the borders of an utter desert, will competition
cease. The land may be extremely cold or dry, yet there will be
competition between some few species, or between the individuals of
the same species, for the warmest or dampest spots.
Hence, also, we can see that when a plant or animal is placed in a new
country amongst new competitors, though the climate may be exactly the
same as in its former home, yet the conditions of its life will
generally be changed in an essential manner. If we wished to increase
its average numbers in its new home, we should have to modify it in a
different way to what we should have done in its native country; for
we should have to give it some advantage over a different set of
competitors or enemies.
It is good thus to try in our imagination to give any form some
advantage over another. Probably in no single instance should we know
what to do, so as to succeed.
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